Mold and process of making same



Patented June 14, 1938 UNITED STATES PATENT OFFICE No Drawing. Application June 29, 1936,

Serial No. 87,958

7 Claims.

This invention relates to improvements in processes of molding castings and facings for molds. An object of the invention, among others, is the provision of a facing for green molds so as to render thesame capable of giving desired results in finished castings with respect to pattern trueness, surface smoothness and sectional soundness, especially in respect to complicated pattern design; in other words, to make relatively inexpensive green molds capable of substitution for more expensive dry sand molds and metal molds heretofore regarded as indispensable in many fields, as for instance, in the field of heavy weight castings and castings of complicated pattern design.

Generally speaking, as is well known in the foundry art, there are two major methods of preparing non-metallic molds for metal casting. There are many variations of these two general methods. but in the main, they are divided essentially into dry sand molding and green molding. Dry sand molding. generally speaking, is a method of preparing sand molds by baking or otherwise drying the excess moisture in the sand before pouring the molten metal into the mold. and green sand molding is a method of using the sand mix with varying amounts of moisture without baking or drying inthe sand mold section before molten metal is poured into the mold. Green sand molds have been found useful in some cases with respect to medium weight castings of medium section without complicated pattern design, but dry sand molding methods have been regarded as indispensable in the field of complicated pattern design and heavy weight castings and where pattern trueness, surface smoothness and sectional soundness is requisite.

Dry sand molding, vantage that it isexpensive because it necessitates costly drying equipment, fuel and often expensive particular facings and partings to withstand the rigors of preheating in a drying oven. The use of the dry sand mold also involves, in addition, expensive drying equipment, such as ovens, also auxiliary equipment, fuel oil, reservoir pumps, lines, and burners, in addition to the labor and time and storage of molds.

By making the relatively inexpensive green sand molds capable of substitution. for the expensive dry sand molds, the green mold eliminates the expensive drying equipment and other items of expense, including those mentioned, which will be manifest to those familiar with the art, in addition to making a saving in respect to time, labor, costs and storage. Heretofore, as

however, has the disadstated: green molds have not been capable of substitution for other molds, such as dry sand molds, because for one thingthe greensand molds, as.used, have contained moisture, and it is well known in the foundry art that when green sand mold surfaces contact molten metal hot enough to decompose water or any other volatile matter into its component gases, which occupy muchgreater volume than when in a liquid or solid state, there result disturbances not only to 10 the newly forming metallic skin of the solidifying casting but also disturbances to the smooth sand mold surface resulting in the defect best known as burning in" of the sand into the metal surface of the casting due to intermingling of the loosening sand grains into molten or semi-molten matter.

By my invention I have succeeded in making cheap green molds available for purposes for which more expensive molds have been considcred indispensable. I

Another object in particular among others has been. to eliminate expensive baking and drying and not only is the expensive baking and drying eliminated but a better casting is obtained which requires no finishing and this is particularly true in the field of intricately shaped castings.

Another object has been safety, and by my invention I have eliminated any danger from explosive gases, and in addition, there is no dis- 3 0 turbance of the metal surface due to gases. In accordance with my invention, I make up a sand mold section, made preferably of silica sand of a grain size, large enough to obtain a proper permeability to vent out generative gases evolved while casting, which may be either crude or washed and dried. I preferably use from ninetyfour to ninety-eight and one-half per cent. by weight of the silica sand and bond the same to-- gether with from five per cent. to one-half per cent. by weight of a highly colloidal clay-like material such as bentonite and about one per cent. of water by weight. Upon the face of a green sand mold section so made without baking or drying I apply a parting agent made up ofa fine dispersion of a highly colloidal clay-likematerial in water, such. as an aqueous solution of bentonite. This may be sprayed or brushed on the surface of the mold in a thin film, the thickness and viscosity of which will depend on conditions found to be proper to meet the demands of temperature, by cycle, and casting weight. and shape, and this aqueous solution of bentonite may employ from one-half per cent. to seven per cent. by weight of bentonite,

. and ninety-three to ninety-nine and one-half per cent. water. On the surface of this parting agent just described I apply by spraying from a spray gun or otherwise, a refractory facing which consists preferably of some such substance as twohundred mesh silica flour or one hundred forty mesh, seventy-two hour, pulverized coke. The

fiour or coke may be of a coarse mesh and may be applied immediately. The molten metal may then immediately be poured into the mold and. when desired may easily be removed and it will be found that the green sand mold used according to my process has produced a perfect casting without any need for the usual finishing operation.

As has been stated, the moisture in green sand molds has presented a problem in that the molds have contained moisture and when the mold surface contacted the molten metal hot enough to decompose water into its component gases occupying much greater volumethan when in a liquid or solid state, disturbances resulted with respect to the sand mold and the casting known as "burning in. I have eliminated this by means and method described.

The parting agent is a plastic and isadhesive at ordinary temperatures but changes its form with rises in temperature. While it is a gel at ordinary temperatures'such as room temperatures and acts as a binder, and while it changes to a plastic glass-like substance at higher temperatures continuing to act as a binder, at still higher temperatures produced by the molten metal the parting agent takes on a crystalline or powder-like form and loses its binding property, the parting agent falling apart and permitting the easy withdrawal of the casting at the same time, at all times functioning to separate the sand mold surface from the casting surface.

The temperature at which these changes take place will vary somewhat, depending manifestly on, for example, variations in bentonite and impurities. However, for example, in certain cases the change from the plastic to the. glass-like state may occur at around eight hundred degrees Fahrenheit, and the change from the glass-like state to the powder state may occur at around seventeen hundred degrees Fahrenheit.

My invention is not limited to bentonites, although I have found they give the best result. I have found that Welsh Mountain clay from the Welsh Mountains in Pennsylvania will give a good result, but not as efficient for certain purposes as bentonite. Other high colloidal clays may be used, and instead of coke and flour for the facing,

plumbago or graphite or other carbonaceous or silicious material in powdered form may be used; and of course, proportions may be changed for different conditions, as will be readily apparent to those skilled in the art.

WhileI have described the preferred form and steps for carrying my invention into effect, these are capable of variation and modification without departing from the spirit of the invention. I, therefore, do not wish to be limited to the precise details set forth but desire to avail myself of such variations and modifications as come within the scope of the appended claims.

Having thus described'my invention, claim as new and desire to secure by Letters Patent is:

1. In molding means a sand mold, a plastic and adhesive coating for said mold consisting. of anaqueous solution of bentonite which is in the form of a gel at ordinary temperatures and acts what I as a binder and which takes on a crystalline form and loses its binding property at higher temperatures, and a pulverulent facing applied to said coating as a separate layer, said adhesive coating functioning to bind the facing to the mold at ordinary temperatures and functioning so as not to bind the facing at high temperatures.

2. In molding means a sand mold, a plastic and adhesive coating for said mold consisting of an aqueous solution of bentonite employing substantially about one-half of one per cent. to seven per cent. by weight of bentonite and ninetythree to ninety-nine and one-half per cent. by weight of water which is in the form of a gel at ordinary temperatures and acts as a binder and which takes on a crystalline form and loses its binding property at higher temperatures, and a pulverulent facing applied to said coating as a separate layer, said coating functioning to bind the facing to the mold at ordinary temperatures and functioning so as not to bind the facing at high temperatures.

3. In molding means a sand mold, a plastic and adhesive coating for said mold consisting of an aqueous solution of bentonite which is in the form of a gel at ordinary temperatures and acts as a binder and which takes on a crystalline form and loses its binding property at higher temperatures, a pulverulent facing applied to said coating as a separate layer, said coating functioning to bind the facing to the mold at ordinary temperatures and functioning so as not to bind the facing at high temperatures, and molten metal poured in said mold on said facing and coating in its gel form.

4. In molding means a green sand mold, a plastic and adhesive coating for said mold consisting of an aqueous solution of bentonite which and acts as abinder and which takes on a crystalline form and loses its binding property at higher temperatures, and a pulverulent facing applied to said coating as a functioning to bind the facing to the mold at ordinary temperatures and functioning so as not to bind the facing at high temperatures.

5. The process of molding castings which includes first applying to a mold a plastic and adhesive coating of an aqueous solution of bentonite which is in the form of a gel at ordinary temperatures and acts as a binder and which takes on a crystalline form and loses its binding property at high temperatures, secondly applying a pulverized facing to said coating in its gel state, said coating functioning to bind the facing to the mold at ordinary temperatures and functioning so as not to bind the facing at high temperatures, and then pouring molten metal into said mold on top of said facing and said gel coating.

6. The process of molding castings which first includes applying to a mold a plastic and adhesive coating of an aqueous solution of bentonite consisting of about one-half of one per cent. to seven per cent. by weight of bentonite and ninety-three to ninety-nine and one-half per cent. by weight of water-which is in the form of a gel at ordinary temperatures and acts as a binder and which takes on a crystalline-form and loses its binding property at high temperatures, secondly applying a pulverized facing to said coating in its gel state, said coating functioning to bind the facing to the mold at ordinary temperatures and functioning so as not to bind the facing at high temperatures, and then pouring molten metal into said mold on top of said facing and said gel coating.

separate layer, said coating '7. The process of green sand molding castings state, said coating functioning to bind the facing which includes first applying to a mold'a plastic to the mold at ordinary temperatures and funcand; adhesive coating of an aqueous solution of tioning so as not to bind the facing at high bentonite which is in the form of a gel at ordinary temperatures, and then pouring molten metal into temperatures and acts as abinder and which. said mold on top of said facing and saidgel 5 takes on a crystalline form and loses its binding coating. property at high temperatures, secondly applying a pulverized facing to said coating in its gel WILLIAM HENRY OWEN. 

